The present invention relates to a liquid crystal display unit and a wiring structure of the liquid crystal display device, and particularly to an active matrix type liquid crystal display device (AM-LCD) which is driven by many thin-film transistors (TFT) and a wiring structure of the active matrix type liquid crystal display device.
In recent years, a thin-film transistor driving liquid crystal display device (TFT-LCD) is used as a liquid crystal display device which can be made thin in size, light in weight and high in definition, and the market of the thin-film transistor driving liquid crystal display device is gradually being expanded compared to that of the conventional display device using a cathode-ray tube.
The thin-film transistor driving liquid crystal display device is constructed by forming a plurality of parallel gate wires, a plurality of parallel data wires intersecting with the plurality of gate wires, a plurality of thin-film transistors each arranged near each of the intersections of the parallel gate wire and the parallel data wire, pixel electrodes each connected to each of the thin-film transistors, gate insulator films each covering a gate of each of the thin-film transistors and a protective film covering exposed portions of each of the thin-film transistor on a first substrate (a glass substrate); and by placing a second substrate (a glass substrate) opposite to the first substrate; and by putting a liquid crystal layer between the first substrate and the second substrate arranged opposite to each other. In regard to such a thin-film transistor drive liquid display device, as needs of large display screen and high definition are growing more in recent years, the requirements of specifications to the thin-film transistor drive liquid display device such as necessity of reducing resistance of the parallel gate wiring and the parallel data wiring, necessity of increasing the manufacturing yield at manufacturing the display devices and so on become severer.
In order to reduce the resistance of the parallel gate wiring and the parallel data wiring, it is necessary to employ a material having a low resistivity as the wiring material. As such a material, aluminum (Al), copper (Cu), silver (Ag) or an alloy containing any one of the above elements as a major constituent is known. However, as reported, for example, in Journal of the Electrochemical Society, 137 (1990), pp. 3928-3930, it is well known that these low-resistance wiring materials are large in contact resistance with indium-tin oxide (ITO) which is generally used for connecting terminals of the parallel gate wiring and the parallel data wiring, and accordingly, it is impractical to directly connect the low-resistance wire to the indium-tin oxide terminal. Therefore, a clad structure, in which the parallel gate wiring and the parallel data wiring made of the low-resistive wiring material are coated with the other metallic material, is formed so that the other material may bear the contact property with the indium-tin oxide and the low-resistive wiring material may bear the low resistive property of the parallel gate wiring and the parallel data wiring. Such a clad structure is disclosed, for example, in Japanese Patent application Laid-Open No.9-26602.
In general photolithography is used to form such a clad structure, and it is necessary to perform the two processes of photolithography in total, that is, one process for the low-resistive wiring material and the other process for the other metallic material, which makes the manufacturing process complicated. Therefore, in order to simplify the manufacturing process, a wiring pattern of the laminated structure is formed by a method of continuously forming a laminated layer of a film made of aluminum or aluminum alloy and a film made of the other metallic material through a single process of photolithography. The laminated structures formed through methods similar to the above are disclosed, for example, in Japanese Patent Application Laid-Open No.11-74537, Japanese Patent Application Laid-Open No.6-281954, Japanese Patent Application Laid-Open No.4-240824, Japanese Patent Application Laid-Open No.4-20930 and Japanese Patent Application Laid-Open No.10-240150.
The thin-film transistor drive liquid display device needs to use wiring materials having a low resistivity as the need of high definition is growing more. In such a case, in regard to the thin-film transistor drive liquid display device up to the definition of ultra extended graphics array (hereinafter, referred to as UXGA) (1600xc3x971200), the thin-film transistor drive liquid display device without unevenness of color can be manufactured with a high manufacturing yield by using an aluminum group wiring material and setting the wires to an appropriate thickness (about 200 nm). However, in regard to the thin-film transistor drive liquid display device having a finer definition above quadrable extended graphics array (hereinafter, referred to as QXGA) (2048xc3x971536), troubles such as unevenness of color or the like caused by the wiring resistance are occur when an aluminum group wiring material is used for the wiring material of the thin-film transistor drive liquid display device. In this case, if the thickness of the wiring is increased in order to reduce the wiring resistance, the coverage of the insulator film covering the wires is degraded and accordingly the manufacturing yield is decreased. In order to solve this problem, it is necessary to employ a metallic material having a resistivity lower than that of the aluminum group wiring material, for example, silver or an alloy containing silver as the major constituent.
Although the thin-film transistor drive liquid display device which uses silver for the low-resistive wiring material and has the clad structure of cladding the wiring with the other metallic material is known, as described above, it is required to perform two processes of photolithography in order to form the clad structure. As far as such a means is used, the manufacturing process becomes complicated, and the thin-film transistor drive liquid display devices cannot be manufactured in low cost, and accordingly low-cost thin-film transistor drive liquid display devices cannot be supplied to the market.
The present invention has been made from the viewpoint of the technical background described above, and an object of the present invention is to provide a wiring structure in which a laminated film composed of a film made of silver or an alloy containing silver as the major constituent and a film made of the other metallic material is formed, and a wiring pattern is formed through a single process of photolithography.
Another object of the present invention is to provide a liquid crystal display device which can be manufactured in low cost by forming the laminated film composed of a film made of silver or an alloy containing silver as the major constituent and a film made of the other metallic material and by forming a wiring pattern through a single process of photolithography.
In order to attain the object described above, the wiring structure in accordance with the present invention has a first structure which comprises a plurality of first parallel wires; a plurality of second parallel wires intersecting with the first parallel wires; and a plurality of active elements, each of the active elements being arranged at a position near an intersection of the first parallel wire and the second parallel wire and connected to the first parallel wire and the second parallel wire, wherein part or all of the first parallel wires and the second parallel wires are of a laminated structure of a layer made of silver or an alloy containing silver as a major constituent and a layer made of a metallic element having a standard electrode potential of dissolution reaction lower than the standard electrode potential of silver or an alloy containing said metallic element as a major constituent, and are formed through a single process of photolithography.
According to the first structure described above, since the metal capable of being etched together with silver or the alloy containing silver as the major constituent and having a standard electrode potential of dissolution reaction lower than that of silver, that is, the metal capable of being anodically polarized by electrochemical reaction during wet etching is selected as the metallic material laminated on a film made of silver or the alloy containing silver as the major constituent, the resistivity of wiring material can be decreased and the cross-sectional shape of the wire can be formed in a forward tapered shape through the electrochemical reaction. Thereby, it is possible to obtain a wiring structure of a liquid crystal display device in which the coverage of insulator film on the wiring can be secured.
Further, in order to attain the object described above, the wiring structure in accordance with the present invention has a second structure which comprises a plurality of first parallel wires; a plurality of second parallel wires intersecting with the first parallel wires; and a plurality of active elements, each of the active elements being arranged at a position near an intersection of the first parallel wire and the second parallel wire and connected to the first parallel wire and the second parallel wire, wherein part or all of the first parallel wires and the second parallel wires are of a three-layer laminated structure of a bottom layer made of a metallic element having a standard electrode potential of dissolution reaction lower than the standard electrode potential of silver or an alloy containing the metallic element as a major constituent, an intermediate layer made of silver or an alloy containing silver as a major constituent and a top layer made of a metallic element having a standard electrode potential of dissolution reaction lower than the standard electrode potential of silver or an alloy containing the metallic element as a major constituent, and the three-layer laminated structure is formed through a single process of photolithography.
According to the second structure described above, since the metal capable of being etched together with silver or the alloy containing silver as the major constituent and having standard electrode potential of dissolution reaction lower than that of silver, that is, the metal capable of being anodically polarized by electrochemical reaction during wet etching is selected as the metallic material laminated on a film made of silver or the alloy containing silver as the major constituent, the resistivity of wiring material can be decreased and the cross-sectional shape of the wire can be formed in a forward tapered shape through the electrochemical reaction, similarly to the first structure. Thereby, it is possible to obtain a wiring structure of a liquid crystal display device in which the coverage of insulator film on the wiring can be secured.
Further, in order to attain the other object described above, the liquid crystal display device in accordance with the present invention has a third structure which comprises a first substrate and a second substrate arranged opposite to each other; a plurality of parallel gate wires; a plurality of parallel data wires intersecting with the parallel gate wires; a plurality of thin-film transistors each arranged at a position near each of the intersections of the parallel gate wires and the parallel data wires, the thin-film transistor being connected to the corresponding parallel gate wire and the corresponding parallel data wire; and gate insulator films each covering the parallel gate wire, the parallel gate wires and the parallel data wires and the thin-film transistors and the gate insulator films being formed on one surface of the first substrate; and a liquid crystal layer put between the first substrate and the second substrate, wherein at least one of the parallel gate wiring and the parallel data wiring has the first or the second wiring structure.
According to the third structure described above, since the wiring structure of the first structure or the second structure is used in at least one of the parallel gate wiring and the parallel data wiring, at least one of the resistance of the parallel gate wiring and the resistance of the parallel data wiring can be reduced, and at the same time the cross-sectional shape of the wire can be formed in a forward tapered shape through the electrochemical reaction. Thereby, it is possible to secure the coverage of insulator film on the wiring, and to obtain the thin-film transistor liquid crystal display device with a high manufacturing yield.
Further, in order to attain the other object described above, the liquid crystal display device in accordance with the present invention has a fourth structure which comprises a first substrate and a second substrate arranged opposite to each other; a plurality of parallel gate wires; a plurality of parallel data wires intersecting with the parallel gate wires; a plurality of thin-film transistors each arranged at a position near each of the intersections of the parallel gate wires and the parallel data wires, the thin-film transistor being connected to the corresponding parallel gate wire and the corresponding parallel data wire; gate insulator films each covering the parallel gate wire; and transparent electrodes to be used as connecting terminals for at least one of the parallel gate wiring and the parallel data wiring, the parallel gate wires and the parallel data wires and the thin-film transistors and the gate insulator films and the transparent electrodes being formed on one surface of the first substrate; and a liquid crystal layer put between the first substrate and the second substrate, wherein at least one of the parallel gate wiring and the parallel data wiring has the first or the second wiring structure, and the transparent electrode is made of a material selected from the group consisting of a mixed oxide of indium oxide and zinc oxide, and a mixed oxide of indium oxide and germanium oxide.
According to the fourth structure described above, the wiring structure of the first structure or the second structure is used in at least one of the parallel gate wiring and the parallel data wiring, and the transparent electrode is made of a material selected from the group consisting of a mixed oxide of indium oxide and zinc oxide, and a mixed oxide of indium oxide and germanium oxide. Therefore, at least one of the resistance of the parallel gate wiring and the resistance of the parallel data wiring can be reduced, and at the same time the cross-sectional shape of the wire can be formed in a forward tapered shape through the electrochemical reaction, and the transparent electrode can be formed without corroding silver or the alloy containing silver as the major constituent. Thereby, it is possible to secure the coverage of insulator film on the wiring, and to obtain the thin-film transistor liquid crystal display device with a high manufacturing yield.
In the first structure to the fourth structure described above, molybdenum (Mo) is the most suitable metal for the metallic capable of being etched together with silver and the alloy containing silver as the major constituent and having a standard electrode potential of dissolution reaction lower than the standard electrode potential of silver.